1. Field of the Invention
The present invention relates to the field of radio communication apparatus such as mobile telephones, portable telephones, cordless telephones, pagers, and the like. More specifically, the present invention relates to a radio communication apparatus intermittently powered by a battery.
2. Description of the Related Art
In general, radio communication devices used in radio systems are battery powered. Because batteries have a limited power capacity, it is necessary to reduce the power consumed by the radio communication devices in order to preserve their batteries.
For example, the power consumed by pagers in a conventional paging system is reduced in order to prevent battery wear in the following manner. The pagers are divided into several groups. The supply of power from a battery to a radio receiver section of a pager is periodically turned off. The power supply is turned on only to receive paging signals directed to the group to which the pager belongs.
FIG. 1 shows a known signal format used in a paging system with a conventional battery saving function. Referring to FIG. 1(a), all pagers in the system are divided into n groups, for example, 15 groups. A base station repeatedly broadcasts a frame signal consisting of n group signals. Each group signal includes preamble words and m paging words (FIG. 1(b)) where m is 20. The preamble word includes a predetermined signal sequence for synchronization of received signals and a group designation signal (an intermittent reception control signal) for designating the group of pagers to which the associated paging words are addressed. Each paging word includes data bits and check bits (FIG. 1(c)). The data bits consist of x bits and the check bits consist of y bits. The data bits represent an identification number of paged (called) pagers. The check bits correct any error occurring in the data bits. The paging word consisting of data bits and check bits may be a so-called (31, 16) BCH code in which 15 check bits are appended to 16 data bits.
A base station receives a paging request to a pager from a landline telephone via a paging exchange. In response thereto, the base station inserts an identification number corresponding to the paged pager into the data bits of one of the paging words when broadcasting the paging words of the group to which the pager belongs. If a pager belongs to group 2, the pager automatically turns on the power supply to its radio receiver section only when paging words for group 2 are broadcast. Paging words are broadcast periodically at a predetermined time interval (once per frame). Once the pager synchronizes to the timing schedule at which the paging words of group 2 are broadcast, the power supply to the radio section is thereafter automatically and repeatedly turned on and off. This results in a cyclic, intermittent power supply to the pager.
A problem with the conventional battery saving technique employed in a radio communication apparatus is that all of the circuits in the apparatus are simultaneously supplied with power in synchronism with the control signal transmitted from the base station. In general, a radio communication apparatus has a variety of circuits. The time period required for a circuit to be rendered operative varies depending on the characteristics of the circuit. For example, a synthesizer circuit needs more time to output a stabilized synchronization signal than other circuits. Circuit characteristics are not considered in the conventional battery saving technique.